[Josh Grisdale]

My guess (only a guess) is that a lot are very old sites and may just be http not https and many modern browsers warn you it is dangerous.

Or possibly the site no longer exists and the page listing it hasn’t updated links…

Can you either provide a screenshot of the error or maybe share one or too links that you tried? (Don’t share too many or you may get blocked as spam when posting to tabifolk.)